Method for the production of a fibrous sheet material

ABSTRACT

A method for the production of a fibrous sheet material by passing a stream of gas containing suspended fibres through a gaspermeable forming surface to form a fibrous layer thereon and bonding the fibres to each other or to a reinforcing material by means of a foamed binder.

United States Patent [191 Rasmussen et al.

[ METHOD FOR THE PRODUCTION OF A FIBROUS SHEET MATERIAL Inventors:Torben Borup Rasmussen, Tousvej;

Kjeld Dossiug Ottosen, l-lolmevej; Torsten Bengt Persson, Lystrup, allof Denmark Karl Kristian Kobs Kroyer Vestre Kongevej, Aarhus-Viby,Denmark Filed: Nov. 14, 1968 Appl. No.: 776,859

Assignee:

[30] Foreign Application Priority Data Nov. 15, 1967 Denmark 5701/67[52] US. Cl. 156/62.2, 156/78 [51] Int. Cl B32b 23/12 [58] Field ofSearch 156/72, 78, 79, 62.2; 264/ 121 [56] References Cited UNITEDSTATES PATENTS 3,158,668 11/1964 Johnson 264/121 Primary ExaminerReubenEpstein Attorney-Watson, Cole, Grindle and Watson [57] ABSTRACT A methodfor the production of a fibrous sheet material by passing a stream ofgas containing suspended fibres through a gaspermeable forming surfaceto form a fibrous layer thereon and bonding the fibres to each other orto a reinforcing material by means of a foamed binder.

4 Claims, 4 Drawing Figures Pmminumsolsrs I 3.769.115 sum 10F 3PAIENTEDncI 30 ms 3,769,115 SHEET 20F 3 ATTORNEY PAIENTEUnmso 19153,769.1 1s SHEET 3 [IF 3 METHOD FOR THE PRODUCTION OF A FIBROUS SHEETMATERIAL BACKGROUND OF THE INVENTION This invention relates to a methodfor the production of a fibrous sheet material by passing a stream ofgas containing suspended fibres through a gaspermeable forming surfaceto form a fibrous layer thereon and bonding the fibres to each other orto a reinforcing material by means of a binder.

In the production of fibrous sheet materials by the well known wetprocess which is used within the paper industry hydrogen bonds betweenthe fibres are created during the formation of the fibrous layer fromthe aqueous suspension f fibres. These hydrogen bonds ensure togetherwith the binder good strength properties of the final wet processproducts.

When preparing similar products in a dry'process no or only a fewhydrogen bonds are created because the dry fibres which are veryirregular do not get into so close contact that hydrogen bonds betweenthe fibres can be established. Consequently, the type of binder and theway in which said binder is applied to the fibrous material are of greatimportance for obtaining the desired strength of the end productsprepared by a dry process.

It has been attempted to apply the binder to the fibrous product as amist generated in one or more spray nozzles. This form of applicationhas many advantages but also many drawbacks. Thus, one of the drawbacksis that is is difficult to obtain a uniform distribution of said binder.Furthermore, a spraying cabin with a suction device is necessary inorder to prevent the escape of binder particles which may stick to otherparts of the apparatus and which may also be injurious to the health ofthe operators. Finally, it is necessary to clean the spray nozzles whichtend to be choked at regular intervals.

Also an impregnating technique has been used. Such a technique presentsthe advantage that the binder penetrates deeper into the material thanwhen the binder is sprayed onto the fibrous material. Furthermore, bothsides of the product can be treated in one step. How'- ever, a method ofimpregnating has the drawback that great amounts of solvent such aswater are introduced into the product and consequently, special measuresfor removing said solvent are required.

It is the object of the present invention to improve the well knownmethods of applying a binder to a fibrous material.

SUMMARY OF THE INVENTION According to the invention the binder used is afoamed binder.

One of the most important advantages realized by using a foamed binderis that it may be applied to the fibrous material with a considerablylower content of solvent than by the impregnating method and at the sametime the dosage and the distribution of the binder can easily becontrolled.

By using a foamed binder the health problems which are encountered whenspraying the binder onto the fibrous material are avoided.

The size of the foam bubbles is important because the smaller the foambubbles are the more coherent the layer of binder will be. The size ofthe bubbles depends not only on the manner in which the foam has beenproduced but also on the additives used. As an example of such anadditive, foam stabilizers may be mentioned.

When using a reinforcing net as the gaspermeable forming surface toobtain an end product comprising said reinforcing net a foamed bindermay be applied to the net before the application of the fibres.

The use of a foamed binder consisting of very small bubbles results in acomplete encirclement of the threads of said net by the binder. This isespecially advantageous if certain types of synthetic fibre scrims areused as reinforcing material because it is very difficult to cause thebinder to adhere to the threads of said synthetic fibre scrims.

' The foamed binder is preferably applied to the fibrous sheet materialby passing said sheet material through a trough-like funnel, the bottomof which comprises two lips adjustable relative to the plane in whichthe fibrous sheet material is passed through said funnel. When fillingthe foam into such a funnel the binder is automatically applied to thesheet material as it moves through said funnel.

' The application of binder to the surface of the sheet material willoften'be insufficient to avoid a delamination of said sheet material.Thus, the binder should be introduced into the fibrous material itself.According to the invention the tendency of delamination is avoided bysucking or pressing the foam applied into the fibrous layer. Whensuction is used it is preferred that the sheet material after a foamlayer has been applied is passed over a suction box to cause the binderto penetrate the fibrous layer.

The application of the foam layer is preferably carried out by passingthe fibrous layer under an inclined doctors knife and by introducing thefoam under said knife. To avoid an undesirable reduction of thevoluminosity of the fibrous materialthe pressure exerted by saidscraping knife should not be too high.

The foamed binder may be pressed into the fibrous material by mechanicalmeans.

By using a foamed binder having a ratio of binder volume to gas volumeof about 1:17, 20 grams of binder on dry basis may be applied per metreof fibrous material.

In a preferred embodiment of the method according to the invention areinforcing net material is used and.

a layer of binder is subsequently applied to both sides of saidreinforcing net material, whereafter fibrous layers formed by passing astream of gas containing suspended fibres through ,a g'aspermeablesurface to form a fibrous layer thereon are applied to both sides ofsaid reinforcing net material, whereafter the product thus formed issubjected to a compression.

By applying a binder onto the reinforcing net material an improvedpenetration of the binder into the fibrous layer can be obtained and atthe same time avoid the use of a means to be brought into direct contactwith the binder otherwise necessary for the further treatment of theproduct. This method is particularly suitable when the fibrous layersused have many free fibre ends. By bringing these fibre ends in contactwith the reinforcing net material a bonding similar to that of a zipfastener is obtained and the strength of the product is consequentlyincreased.

The compression is preferably carried out by passing the reinforcing netmaterial and the fibrous layers applied thereto through slots in the topand the bottom of a closed box and by supplying air under pressure tothe box at both sides of the fibrous sheet material. The air streamsthus created compress the material and contact between the fibrous sheetmaterial and the apparatus used is avoided.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENTS.

The apparatus shown in FIG. 1 comprises two hammer mills each mounted atthe top of a shaft 2. Suction boxes 2 which are connected with suctionpipes 4 are mounted below the bottom of said shafts 2. The upper run ofan endless perforated belt 5 mounted for rotation on two rollers 6 islocated in the area between the lower edge of the shaft 2 and thesuction box 3. The apparatus shown also comprises a roller 7 on which areinforcing net material 8 is wound. The net material is passed througha trough-formed funnel 9 having at its bottom two adjustable lips 10.The apparatus also comprises two endless screens 11 mounted on rollers12 and a set of embossing rollers 13.

The operation of the apparatus is as follows:

Two fibrous layers are formed on the endless belts 5 and aresubsequently passed onto the screens 11. The two fibrous layers aresubsequently brought into contact with the reinforcing net material 8,to which a foamed binder has been applied on both sides in thetrough-shaped funnel 9. When passing between the vertical runs of thescreens 11 the fibrous layers are pressed against the reinforcing netmaterial without bringing the screens into direct contact with thebinder applied.

The composite product is then passed into the nip between the set ofembossing rollers 13 which maybe heated to obtain a final curing of thebinder. The binder used may also be of an expanding type and may beactivated when the composite fibrous product is in the area between thevertical runs of the screens 13, for example by supplying heat to saidscreens.

By proper adjustment of the lips of the troughshaped funnel thethickness of the foamed layer applied to the sides of the reinforcingmaterial can be con trolled.

Another way of applying a foamed binder onto a fibrous sheet material isshown in FIG. .2, which shows an apparatus comprising an endlessgaspermeable screen which is mounted on two rollers 21. An inclinedscraper plate 22 is located above said screen. A suction box 24 which isconnected with a suction pipe 25 is mounted below the upper run of thescreen 20. The operation of the apparatus shown is as follows:

A fibrous layer is introduced on the screen in the direction shown onthe drawing and is caused to pass under the scraper plate 22. A foamedbinder 23, which is continuously supplied to the area below saidinclined scraper plate 22, is then applied to the surface of the fibrouslayer in an amount which depends on-the distance between the lower edgeof said scraper plate 22 and the screen 20. During the passage acrossthe suction box 24 the binder layer applied is sucked into the fibrouslayer so as to bond the fibres together.

The apparatus shown in FIG. 3 comprises two hammer mills 51 each locatedat one end of a shaft 52. At the opposite end of said shaft 52 a suctionbox 53 is provided and one run of an endless screen 54 mounted on twoparallel rollers 55 moves in a path between the shaft 52 and the suctionbox 53. A reinforcing web material 57 which is wound from a roll 56passes through a trough-formed funnel 58 having a bottom comprising twoadjustable lips 59 forming a slot in the bottom of said funnel. Theapparatus shown also comprises two guide rollers 60 and a compartment 61mounted below said guide rollers 60 and having an upper slot 62 and alower slot 63 located in the same vertical plane. Each end of thecompartment 61 is connected with an air inlet pipe 64 connected with acommon blower not shown. In the compartment 61 a number of screens 65are mounted on both sides of the slots 62 and 63. An endless steel belt66 mounted on three rollers 67, 68 and 69 is located below thecompartment 61. The roller 67 co-operates with another roller 70 andsimilarly the roller 68 co-operates with a roller 71. An endless steelbelt is mounted on said rollers 70 and 71.

The apparatus also comprises an auxiliary endless belt 72 mounted on tworollers 73 and 74 and two guide rollers 75 and 76.

The apparatus shown operates in the following manner:

.A gas stream containing suspended fibres are supplied to the hammermills 51 from which they pass into the shafts 52. By means of thesuction boxes 53 firous layers'are deposited on the screens 54. Thesefibrous layers are passed down between the guide rollers 60 and at thesame time the reinforcing net material 57 is passed through thetrough-shaped funnel 58, in which foamed binder is applied to bothsides. The two fibrous layers and the reinforcing material are thenunited in the compartments 61, in which streamsof air are directedagainst the composite material from both sides. When theweb has passedthrough the compartment 612 it is introduced in the nip between therollers 70 and 67 and subsequently between the nip of the rollers 71'and68. During the further movement between the endless belts 66 and 72 thefibrous web material may be heated, e.g., by resistance heating of oneof the belts. Thus, the binder applied to the reinforcing net has beenpartially cured when the web material passes into the nip between therollers 75 and 76.

By blowing oppositely directed streams of air against the compositematerial in the compartment 61 through air inlets 64 the fibrous layersare pressed into contact with the net without using mechanical means. Inthe construction shown a compression of the fibrous layers and thereinforcing net is obtained even when the streams of air introduced inopposite ends of the compartment is different. In this case the distancebetween the web material and the edge of the compartment in that side ofthe compartment in which the pressure is lowest will be decreased. Thus,the area in which the air supplied can escape to the surroundings willalso be decreased and consequently the air pressure will increase. Thus,after some time the web material will find an equilibrium position.

The apparatus shown in FlG. 4 comprises an endless perforated belt 81mounted on three rollers 82, 83, and

84. A hammer mill 8S and a shaft 86 is located above the belt 81 and onthe opposite side thereof a suction box 87 is mounted. Another hammermill 88 with a shaft 89 and a co-operating suction box 90 are locatedbetween the rollers 83 and 84. A reinforcing net material 91 stored on aroll 92 passes over a roller 93 and through a trough-formed funnel 94containing a foamed binder 95. At the lower end of the funnel 94adjustable lips 96 are provided controlling the amount of binder appliedto the reinforcing net 91 during its passage through the funnel 94.

A layer of fibres is formed on the belt 81 by means of the hammer mill85, the shaft 86 and the suction box 87, and this layer is transportedtowards the rollers 83. At the time the reinforcing net 91 is passedfrom the roll 92 through the funnel 94 in which foamed binder is appliedto both sides of the net. At the roller 83 the fibrous layer formed isunited with the reinforcing net 91 and the composite material is passedinto the area between the shaft 89 and the suction box 90, in which alayer of fibres is deposited on the opposite side of the reinforcing net91. After formation of said fibrous layer the product formed can beembossed and the binder can be cured before it is wound up on a roll 97.

The apparatus shown presents the advantage that the fibrous layer formedunder the shaft 86 is thrown against the reinforcing net 91 when said.fibrous layer passes around the roller 83 especially when operating athigh speeds. in this way the fibres are brought into 6 intimate contactwith the binder applied in the funnel 94.

We claim:

1. A method of making a fibrous sheet material consisting of areinforcing net material and at least one layer of short fibers bondedto one another and to the reinforcing net material, the methodcomprising the steps of directing a stream of gas containing suspendedfibers toward a forming surface having apertures therein, allowing thegas to pass therethrough but retaining the major portion of the fibersso as to form on the side of the forming surface to which thefibercontaining gas stream is supplied, a layer of haphazardly locatedfibers, supplying a foamed binder to at least one side of thereinforcing net, and directing the fibrous layer on to the one side ofthe reinforcing net.

2. A method according to claim 1, in which'said foamed binder is rolledinto the fibrous layer. I

3. A method as in claim 1, wherein said binder is applied onto bothsides of said forming surface, that fibrous layers are subsequentlyapplied to said reinforcing net and that the composite product thusformed is compressed.

4. A method as in claim 3, in which the composite material is compressedby passing through slots in the top and the bottom of a closedcompartment in which air streams are directed against the compositematerial from both sides.

1. A method of making a fibrous sheet material consisting of a reinforcing net material and at least one layer of short fibers bonded to one another and to the reinforcing net material, the method comprising the steps of directing a stream of gas containing suspended fibers toward a forming surface having apertures therein, allowing the gas to pass therethrough but retaining the major portion of the fibers so as to form on the side of the forming surface to which the fiber-containing gas stream is supplied, a layer of haphazardly located fibers, supplying a foamed binder to at least one side of the reinforcing net, and directing the fibrous layer on to the one side of the reinforcing net.
 2. A method according to claim 1, in which said foamed binder is rolled into the fibrous layer.
 3. A method as in claim 1, wherein said binder is applied onto both sides of said forming surface, that fibrous layers are subsequently applied to said reinforcing net and that the composite product thus formed is compressed.
 4. A method as in claim 3, in which the composite material is compressed by passing through slots in the top and the bottom of a closed compartment in which air streams are directed against the composite material from both sides. 